This invention relates generally to an isotopic separation process and, more particularly, to isotopic separation processes which employ radial cataphoresis.
The separation of the isotope .sup.235 U (which is fissionable by neutrons) from natural uranium, a mixture containing mainly nonfissionable .sup.238 U, or simply enrichment of the mixture in .sup.235 U are extremely important processes for nuclear applications. The most commonly used process presently being employed on an industrial scale is separation by diffusion through a porous barrier. A number of other processes (electromagnetic separation employing devices derived from the mass spectrometer, for instance the so-called "calutron", separation by centrifugation, by thermal diffusion . . .) have been used or suggested, but have not been employed for large scale operation.
A gaseous diffusion separation stage leads to a separation factor of approximately 1.004. Starting from natural uranium, for which the ratio r = .sup.235 U/.sup.238 U is of the order of 0.7%, the obtaining of a product with an r ratio equal to 3% will necessitate about 1,100 diffusion stages. Thus, any improvement in the efficiency of the enrichment process will effect considerable savings.
As previously mentioned, uranium isotope separation can be accomplished in several ways. Recently, selective photoexcitation which leads to the preferential ionization of a particular isotopic component of a gas mixture has been explored as one process for improving the efficiency of uranium enrichment. Generally, in optical isotope separation schemes there are essentially three principal steps. The first is the preferential absorption of the optical radiation to produce selective excitation or ionization of the atoms or molecules which contain the desired isotopic species. The second step is enhancement of the rates of chemical reactions or physical phenomena which involve the atoms, molecules, or ions containing the desired isotopic species as the result of their preferential absorption and excitation. The third step involves the separation of the resulting atoms, molecules, or ions as the result of the enhancement.
Various procedures for performing the first two steps for optical isotope separation have been explored, and an example can be found in the patent to J. Robieux et al, entitled "Isotopic Separation Process," U.S. Pat. No. 3,443,087, issued May 6, 1969 and the article "Proposed New Method For Separating Isotopes", by Stangeby and Allen, Nature, Vol. 233, p. 472, 1971. The third step introduces a serious problem when a process is scaled to a high throughput for a large-scale separation plant. There are several methods by which this third step can be accomplished employing either photochemical, electric field, or magnetic separation. Photochemical separation introduces additional chemical processing stages not generally required by the other methods. A high density collection of electrons and ions develops space charge in the course of the first two steps which shields an applied electric field. Therefore, the field does not easily penetrate the ionized gas to drive the ions toward an appropriate output channel. In time, of course, the field in a static volume of gas will penetrate as charged particles diffuse out of and are removed from the region of interest. However, for a high throughput commercial system, a quasi-neutral ionized cloud will continuously be present which will, in effect, function to shield the electric field. Alternatively, the ions can be deflected from the gas stream in a commercial system by an applied magnetic field instead of an electric field since, in general, a magnetic field will penetrate a plasma. However, to generate a magnetic field requires considerably more power than an electric field, which is easier to establish, and therefore will affect the overall efficiency of the process. Also, the magnitude of the required magnetic field can be a problem. Higher electric fields can easily be established, whereas higher magnetic fields are difficult to generate in reasonable volumes.
Accordingly, a new process is desired which will efficiently separate out a specific isotope selectively ionized in the course of an isotope separation process.